Examples of power working machines in practical use today include those in which an operating handle is rotatably mounted on a machine body, a throttle lever is mounted on the operating handle for adjustment of an output from a drive source, such as an engine, and a throttle lock lever is also mounted on the operating handle for locking the throttle lever. For practical use, it is only necessary that the power working machines include, in addition to the throttle lever and throttle lock lever, a lock mechanism provided on the machine body for locking the operating handle at a desired rotational angle relative to the machine body and an operation lever (lock-canceling lever) for canceling the locking, by the lock mechanism, of the operating handle. One example of the conventional power working machines is known from Japanese Patent Laid-Open Publication No. HEI-11-28683, which includes the lock mechanism operating in response to human operator's manipulation of a throttle wire.
FIG. 18 hereof illustrates a fundamental construction of the conventionally-known power working machine. The power working machine 200 has a handle structure which includes: an operating handle 202 rotatably mounted on the machine body 201, a throttle lever 203 pivotably attached to the operating handle 202; a throttle lock lever 204 for locking the throttle lever 203; and a lock member 205 that is caused to project, in response to actuation of the throttle lever 203, into abutment against the machine body 201 to thereby stop rotation of the operating handle 202. Namely, a user or human operator can lock the operating handle 202 against the machine body 201 by first disengaging the throttle lock lever 204 from the throttle lever 203 as depicted by arrow b1 and then gripping the throttle lever 203 as depicted by arrow b2 to cause the lock member 205 to project as depicted by arrow b3.
However, with the power working machine 200, the human operator's rotating and locking operation of the operating handle 202 is very cumbersome and complicated because the human operator has to first rotate the handle 202 through a desired rotational angle relative to the machine body 201, disengage the throttle lock lever 204 from the throttle lever 203 and then grip the throttle lever 203 to thereby press the lock member 205 against the machine body 201 so as to lock the handle 202. Further, because the power working machine 200 is not constructed to allow the human operator to lock the handle 202 at a desired position simultaneously with the disengagement of the throttle lock lever 204 from the throttle lever 203, the machine 200 lacks operational reliability in that trimming blades (not shown) are sometimes undesirably activated prior to the locking, against the machine body 201, of the handle 202 depending, for example, on connection timing of a centrifugal clutch.
Therefore, there has been a demand for a power working machine which allows the human operator to rotate the operating handle with simple operation and which can reliably prevent human operator's erroneous operation, e.g. by disabling human operator's operation of the throttle lever during rotating operation of the handle and disabling rotating operation of the handle during operation of the throttle lever.
Another example of the conventional power working machines is known from Japanese Patent No. 2997024, which is constructed to prevent cancellation of the locking by the lock mechanism when the human operator has pulled throttle lever. FIG. 19 hereof is a view showing a fundamental construction of the conventionally-known power working machine 300. The power working machine 300 includes: an operating handle 302 rotatably mounted on the machine body 301, a throttle lever 303 pivotably attached to the operating handle 302; a throttle lock lever 304 for locking the throttle lever 303; and an operation lever 305 for locking/unlocking the operating handle 302 with respect to the machine body 301 that is caused to project, in response to actuation of the throttle lever 303. When the human operator disengages the throttle lock lever 304 from the throttle lever 301 and then pulls the throttle lever 301, a distal end portion 306 of the throttle lever 303 prevents the operation lever 305 from being operated by the human operator. However, because, in the power working machine 300, the operation lever 305 is located only within a finger length from the throttle lever 303, the human operator might accidentally touch and thus erroneously operate the operation lever 305.
Therefore, there has been a demand for a power working machine which can prevent the human operator from accidentally touching the operation lever when operating the throttle lever and thereby allows the human operator to perform the rotating operation of the operating handle with enhanced usability or operability.